Cup making machines, such as those manufactured by Paper Machinery Corporation of Milwaukee, Wis., USA are used to make a variety of cups and containers. A typical cup machine for making paperboard cups, for instance, includes a turret having a plurality of mandrels about which the containers are formed. The turret sequentially rotates the mandrels into cooperation with a variety of workstations where numerous cup forming procedures occur.
In an exemplary procedure, a circular bottom blank is cut at one workstation and attached to the end of a mandrel by a vacuum applied through the mandrel. During this procedure, the outside edge or lip of the bottom blank is folded downwardly. At a subsequent workstation, a sidewall blank is wrapped around the mandrel. The sidewall blank is heated and sealed along a seam which runs generally longitudinally along the side of the cup. (Typically the paperboard is coated with a thermoplastic material, such as polypropylene, so the blanks may be heated and sealed together.)
The sidewall blank extends transversely to the bottom blank except along the lip which runs approximately parallel with the sidewall blank. In some applications, the sidewall blank includes a flap extending beyond the lip of the bottom blank, and the bottom edge of this flap is curled over the lip at an incurl station. Then, at a bottom finishing station, the flap is pressed against the lip from an inside recessed area of the bottom of the cup. By heating the thermoplastic material and firmly pressing the sidewall, sidewall flap, and bottom blank lip together, a seal is formed and the cup is provided with a sturdy bottom region having a recessed area.
There also may be other workstations where various additional cup forming procedures are carried out. For example, one station may be used to provide a curl at the top of the cup to provide a more functional drinking container and a better appearance.
At a typical cup bottom incurl workstation, the bottom edge of the sidewall blank flap is first curled inwardly and then directed into the recessed area at the bottom of the cup. In other words, the sidewall blank flap is effectively folded over the lip of the bottom blank. Conventionally, the incurling of the bottom edge of the sidewall blank is accomplished by a plurality of spool-like rollers having a recessed center region configured to force the bottom edge inwardly and then back into the recessed bottom of the cup when the mandrel and the incurl workstation are moved towards one another.
The rollers are relatively small in diameter and are mounted in the incurl workstation on a rotatable roller assembly. The rollers are spaced so the bottom edge of the sidewall blank first contacts an outermost sloped surface of the recessed center region. The surface directs the edge inwardly and then around an arcuate surface and back towards the bottom blank along the innermost sloped surface, innermost being defined as closest to the longitudinal axis of the cup.
During this curling of the sidewall blank flap, the roller assembly is rotated relatively rapidly to move the rollers along the bottom edge to evenly curl the flap into the recessed area around the entire bottom. However, even though this arrangement works relatively well in many applications, the movement of the rollers around the bottom edge can mar the flap area by both destroying the thermoplastic coating and rendering any printing or logos illegible. This is problematic because cup manufacturers often print an identification line on the sidewall blank flap that must remain readable after the cup bottom is formed. The movement of the rollers about the perimeter of the cup bottom can scuff this identification line to a point where it is no longer readable. Thus, it would be advantageous to create an incurl workstation that permitted the bottom flap to be curled over the bottom blank lip and into the recessed area of the cup bottom without marring the identification line or harming the thermoplastic coating.